Phytotoxic Potential of Methyl 4-Hydroxyphenylacetate Against Ageratina adenophora (Spreng.): Mechanistic Insights and Implications for Sustainable Weed Management

Current management of Ageratina adenophora, a highly invasive weed, relies on synthetic herbicides with environmental and resistance risks, necessitating eco-friendly alternatives. This study evaluated seven phenyl derivatives for phytotoxic activity against A. adenophora via in vitro bioassays. Methyl 4-hydroxyphenylacetate exhibited potent herbicidal efficacy, achieving 100% mortality in 2-month-old seedlings at 30 mM, 3-month-old seedlings at 100 mM, and wild adult/6-month-old plants at 200 mM within 48 hours. At 200 mM, the compound reduced CO₂ assimilation by 113.6% and stomatal conductance by 92.2%, indicating severe photosynthetic and transpirational disruption via oxidative stress-mediated chloroplast degradation and stomatal dysfunction. Hormonal profiling revealed significant declines in IAA-ASP, GA1, TZeatin, and TZR, alongside elevated ABA levels, while GA3 remained stable. These hormonal shifts likely drive stomatal closure and metabolic collapse, culminating in plant death. This study provides the first evidence of methyl 4-hydroxyphenylacetate’s dual-action phytotoxicity—targeting both stomatal regulation and hormonal balance—positioning it as a sustainable biocontrol agent for A. adenophora and potentially other invasive weeds.